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Keywords: Microfluidics Lung and intestinal epithelial cells Endothelial cells Blood-brain barrier PermeabilityTrans-epithelial/endothelial electric resistance a b s t r a c t Models of biological barriers are important to study physiological functions, transport mechanisms, drug delivery and pathologies. However, there are only a few integrated biochips which are able to monitor several of the crucial parameters of cell-culture-based barrier models. The aim of this study was to design and manufacture a simple but versatile device, which allows a complex investigation of barrier functions. The following functions and measurements are enabled simultaneously: co-culture of 2 or 3 types of cells; flow of culture medium; visualization of the entire cell layer by microscopy; real-time transcellular electrical resistance monitoring; permeability measurements. To this end, a poly(dimethylsiloxane)-based biochip with integrated transparent gold electrodes and with a possibility to connect to a peristaltic pump was built. Unlike previous systems, the structure of the device allowed a constant visual observation of cell growth over the whole membrane surface. Morphological characterization of the layers was also accomplished by immunohistochemical staining. The chip was applied to monitor and characterize models of the intestinal and lung epithelial barriers, and the blood-brain barrier. The models were established using human Caco-2 intestinal and A549 lung epithelial cell lines, hCMEC/D3 human brain endothelial cell line and primary rat brain endothelial cells co-cultured with primary astrocytes and brain pericytes. This triple primary co-culture blood-brain barrier model was assembled on a lab-on-a-chip device and investigated under fluid flow for the first time. Such a versatile tool is expected to facilitate the kinetic investigation of various biological barriers.